1. Field of the Invention
The present invention relates in general to medical instrumentation, and more particularly to intraluminal devices, and still more particularly to guidewires or core wires for intraluminal devices including catheters.
2. Description of the Prior Art
The use of intraluminal catheters for treatment of various medical problems within the body is well known. It is also well known that a variety of problems are encountered as the catheter is steered through the selected lumen to a desired point within the body. The path may be tortuous and the point of interest may be difficult to locate precisely. To combat this problem, a flexible guidewire may first be inserted into the vascular lumen to the desired location. Once a guidewire is in positioned, a desired catheter may then be slid over the guidewire to reach the desired situs in the body.
It can readily be seen that it is important to have a guidewire that is flexible enough to traverse the tortuous vascular system. It can also be readily be seen that it is also important to have a guidewire that is radioscopic such that the physician can verify the position of the guidewire within the vascular lumen.
A continuing series of technical improvements and additions have been made in the catheter field to provide devices and methods which can overcome certain of the difficulties. One such series of improvements has resulted in the now well known use of a thin flexible guidewire that can be more easily steered through the lumen by forces applied to a proximal section. Because the distal section of a tapered guidewire may lose pushability, another improvement that has been developed is the use of a coiled wire helix which is wrapped around the most distal section of the guidewire. The coiled wire helix may improve the pushability of the distal section of the guidewire while maintaining overall flexibility.
One improvement involving a coiled wire helix is discussed in U.S. Pat. No. 4,619,274 issued to Morrison. Morrison discloses a core member having a proximal and a distal end wherein the core member has a decreasing cross sectional area in a direction towards the distal end. The decreasing cross sectional area is incremental in that the core member comprises a plurality of fixed diameter cylinders which are coupled together by "tapered sections". The diameters of the fixed diameter cylinders become smaller in the direction of the distal end of the core member.
Morrison further discloses a tapered coil which is carried and secured to the core element and extends over the distal extremity of the core element. The tapered coil has a proximal end and a distal end wherein the diameter of the tapered coil decreases in the direction towards the distal end. Furthermore, the coil is formed of wire having a diameter which decreases in the direction towards the distal end. The improvements suggested by Morrison may provide some increased pushability while maintaining a degree of flexibility. However, the decreasing diameter core member and tapered coil may limit the controllability of the distal tip of the core member. Also, the apparatus suggested in Morrison may only provide a single radioscopic intensity level within the vascular lumen.
Another technique involving a coiled wire helix is discussed in U.S. Pat. No. 4,846,186 issued to Box et al. In Box, a core member having an initial uniform diameter segment tapers along a uniform portion to a second constant diameter segment. A flexible spring tip surrounds and is attached to the second constant diameter segment and extends distally therefrom. The core member again tapers in a region where the flexible spring separates from the core member. Within the flexible spring, the core member is flattened to increase the flexibility of the distal portion of the core member. The flattened core and spring are brazed together at an extreme distal tip portion to form a distal guidewire tip. A problem with Box is that the flexibility of the core member is not uniformly increased in the direction of the distal tip. That is, the Box apparatus comprises a plurality of uniform diameter segments coupled together with tapered portions. Therefore, the change in flexibility is isolated to discrete locations along the core member. Another problem with Box is that the radioscopic image has a single radioscopic intensity level within the vascular lumen.
A further approach involving a coiled wire helix is discussed in U.S. Pat. No. 4,971,490 issued to Hawkins. Hawkins suggests a method for providing a smooth transition from the proximal end of the coiled wire helix to the core member. In previous embodiments, the coiled wire helix was wound around the core member thereby creating a ridge at the interface between the coil and the core member. This ridge may cause friction against the vascular lumen as the core member is withdrawn from the vascular lumen. Hawkins provides for a stepped down portion near the distal end of the core member defining a reduced diameter for receiving the proximal end of the coiled wire helix. The reduced diameter is set to be less than the inner diameter of the coil wire helix such that there is a smooth transition between the core member and the coil wire helix. A problem with Hawkins is that the flexibility of the core member changes abruptly at the reduced diameter stepped down portion. Another problem with Hawkins is that the radioscopic image has a single radioscopic intensity level within the vascular lumen.
An additional technique involving a coiled wire helix is discussed in U.S. Pat. No. 4,832,047 issued to Sepetka et al. Sepetka attempts to solve the same problem that Hawkins solved. That is, Sepetka suggests a method for providing a smooth transition from the proximal end of the coiled wire helix to the core member. Sepetka does this by providing a guidewire having a distal tapered segment and having a distal end coil carried over a portion of the tapered segment. The strand forming the helical wrappings of the coil is reduced in thickness in the region of proximal attachment to the core member, thus maintaining a relatively constant sum diameter of the core member and the coil. A problem with Sepetka is that the coiled wire helix is difficult to manufacture. Anther problem is that the radioscopic image has a single radioscopic intensity level within the vascular lumen. Another improvement involving a coiled wire helix is discussed in U.S. Pat. No. 5,174,302 issued to Palmer. Palmer suggests an apparatus wherein the coiled wire helix is banded to define portions that are highly radiopaque and portions that are much less radiopaque to X-radiation. This configuration allows post angioplasty X-ray imaging of the blood vessel without removal of the guidewire. Palmer suggests varying the pitch of stainless steel winding to leave gaps between adjacent coils. Later, highly opaque wire coils are interleaved into these gaps before the spring is mounted into the core member. This is a fairly complex manufacturing process. In addition, the flexibility of the core member is not uniformly increased in the direction of the distal tip. That is, the Palmer apparatus, like Box above, comprises a plurality of uniform diameter segments coupled together with tapered portions.
A coiled wire helix is discussed in U.S. Pat. No. 5,144,959 issued to Gambale et al. Gambale suggests an apparatus wherein there are two coaxial coiled wire helices wrapped around the core member. The inner helix is wrapped around the extreme distal tip of the core member and extending distally therefrom. The inner helix is formed from a highly radiopaque material. The portion of the core member that is disposed within the outer helix is plated with a radiopaque material. When viewed under fluoroscopy, the highly radiopaque coil defines a dark image whereas the more proximal plated portion of the core member defines a moderately radiopaque image. A problem with Gambale is that two separate coils must be used along with an electroplating process. Also, the flexibility of the core member is not uniformly increased in the direction of the distal tip.
A further approach involving a coiled wire helix is discussed in U.S. Pat. No. 5,228,453 issued to Sepetka. Sepetka suggests a guidewire having a torquable proximal wire section, a more flexible intermediate section with a flexible polymer type covering, and a most flexible distal end section having a coiled wire helix wrapped therearound. A helical ribbon coil is wrapped about the intermediate core segment between the core member and the polymer tube covering to increase radiopacity and improve torque transmission while retaining flexibility. A problem with Sepetka is that two wire helices are required along with a polymer covering. Also, the flexibility of the core member is not uniformly increased in the direction of the distal tip.